1. Field of the Invention
This invention relates to impact modification of poly(C.sub.2 to C.sub.8 alkylene terephthalates).
2. Description of the Prior Art
Poly(C.sub.2 to C.sub.8 alkylene terephthalates) are limited in their use as molding resins due to their relatively low notched impact strength at room temperature and below.
The poly(alkylene terephthalates) with the most potential utility as molding resins are the low molecular weight materials, corresponding to a low intrinsic viscosity (IV), because of reduced cost and improved flow properties which are most useful for injection molding. However, decreasing the IV of a poly(alkylene terephthalate) results in loss of notched impact strength as well as a decreased response to previously-suggested impact modifier systems. The use of additives such as mineral fillers and flame retardants tends to further embrittle these plastics.
Various modifier systems for improving the toughness of these thermoplastics have been suggested. Japanese Patent Publication No. 75-48059 of Apr. 28, 1975; German Patent DT No. 2338615 corresponding to U.S. Patent Applications Ser. No. 276,502 of July 31, 1972 now abandoned and Ser. No. 358,778 of May 9, 1973; and Japanese Pat. No. 75-160,365 teach the use of segmented copolyester elastomers as impact modifiers for poly(alkylene terephthalates), the latter further teaching glass fiber reinforcement. An excellent impact modification system comprised of a multiphase composite interpolymer having a first phase polymerized from a monomer system comprised of about 75 to 99.8% C.sub.1 to C.sub.6 alkyl acrylate has been suggested by Farnham and Goldman in U.S. Patent Application Ser. No. 694,509 of June 9, 1976 now U.S. Pat. No. 4,096,202. U.S. Pat. No. 3,919,353 suggested impact modifiers based on rubbers of polybutadiene, butadiene-styrene copolymers, butadiene-acrylonitrile copolymers, ethylenepropylene rubbers, polyisobutene and polyisoprene; and U.S. Pat. No. 3,864,428 teaches the mixture of aromatic polycarbonates and graft copolymers of a butadiene polymer-vinyl monomer as a synergistic impact modification system for poly(alkylene terephthalates).
While some of the prior systems are efficient, the industry still seeks more efficient impact modification systems for poly(alkylene terephthalates).
It is an object of the present invention to provide a more efficient impact modification system for poly(alkylene terephthalates).
It is a further object to provide an improved injection moldable poly(alkylene terephthalate).
A still further object of the present invention is a method for improving the impact strength of poly(alkylene terephthalates).